Marking of objects with codes for identification is commonly used in both industrial and commercial environments. For example, one-dimensional (barcode) and two-dimensional codes have been placed on objects to allow for quick identification of the object based on the data contained in the codes. Generally, laser based scanning devices and systems are used to read the codes due to their ability to successfully scan the code on an object when the object is moved by the scanner quickly. This can allow for laser based scanning devices to have a high scan rate (lines/second), when compared to other scanning devices.
Additionally, laser based systems can be easily commissioned, as a reading area of a laser scanner can be clearly marked by the laser line. This can allow users to quickly determine proper alignments of the laser scanner and peripheral devices. Further, laser scanning devices can have large viewing angles, (e.g. 60-90 degrees). The large viewing angle allows for laser scanners to be mounted very close to the object to be scanned, or the scanning area (i.e. a conveyor belt) while still maintaining sufficient reading area to be able to read a code.
However, laser based devices are subject to multiple regulations, and are generally regulated to limit the amount of energy that the laser can output. This regulation of the laser output power can limit the distances and fields of view (“FOV”) over which the laser based scanning devices and systems can be used. Additionally, many laser based scanning devices utilize rotating or vibrating mirrors to generate a moving spot. These moving parts can subject laser based scanning systems to additional wear and tear, and thereby decrease both reliability and lifespan of the device.
Previously, vision or camera based systems have been used in an attempt to provide an alternate to using laser scanning devices. However, previous vision or camera based systems did not have sufficient scan rates to be able to scan many codes, particularly in applications where the codes are required to be scanned quickly. For example, in an application where the object is moving at approximately 1 m/s, a laser scanner can scan the code at 1000 lines per second. Thus, the code would move only 1 mm between scans. However, a typical vision or camera based system may have a scanning rate of only 30 frames per second, allowing for approximately 33 mm of movement between frames. This can result in missed codes or partially imaged codes, or possibly no capture at all of the code in any of the frames.
Further, in camera or vision based scanning systems, the opening angle of the field of view is determined by the focal length of the imaging lens and the sensor size. Generally, these systems have an opening angle of about 30 degrees to about 40 degrees. These opening angles are generally smaller than for laser based scanning systems. Therefore, for a camera or vision based scanning system to cover the same field of view as a laser based scanning system, the camera or vision based scanning system must be placed farther from the object to be imaged than a laser based scanning system. Thus, a solution for increasing a scanning rate of a vision system is needed.